General anesthetics, a select group of central nervous system depressants, which have the capacity to produce a rapidly reversible loss of consciousness, analgesia and muscle relaxation, are used principally to reduce patient awareness or recall of distressing or painful surgical procedures. Representatives of this group include (1) barbituate derivatives such as Pentothal (sodium thiopental) for intravenous use, (2) volatile liquid inhalation anesthetics such as Fluothane (halothane) and Penthrane (methoxyflurane) and (3) gases such as cyclopropane and nitrous oxide.
Anesthesia produced by either the intravenous or inhalation agents creates a certain degree of risk to the patient. The pharmacologic, physical-chemical and pharmacokinetic properties of these agents require that extreme caution be used when they are utilized for surgical anesthesia. When amounts slightly larger than the anesthetic dose are given, these agents can be lethal. Because of their high lipid solubility, the use of general anesthetics in obese patients can pose a particular problem because larger amounts of drug are required to induce anesthesia. These agents, being retained in fatty tissues, will take longer to dissipate in these individuals. The metabolic conversion products of some anesthetics, especially the volatile liquids, can produce dose related toxicities including liver and kidney damage.
The search for improved general anesthetics continues, as well as the search for means of producing the same therapeutic effect using lesser amounts of the known anesthetic agents. The present invention provides a means of inducing the same degree of anesthesia with less of the anesthetic agent by pre-treating a patient to be anesthetized with a benzopyranopyridine. The benzopyranopyridines have no anesthetic activity themselves. However, when patients are pre-treated with the benzopyrans useful in the practice of this invention, the onset of anesthesia is shortened and duration of anesthesia is significantly lengthened, without increasing the mortality rate. In other words, the same degree of anesthesia can be produced with far less anesthetic agent when a patient is pre-treated with the compounds useful in the practice of this invention.
While it is common to pretreat patients prior to anesthesia, the agents used are not necessarily anesthetics in and of themselves and have no demonstrated synergistic effect on a particular anesthetic. Rather, the pre-anesthetic medications often serve to relax the patient prior to surgery as well as diminish the undesirable side effects common to many general anesthetics.